I see one big value in them, it's alot easier for new Siege players to make money. I show them the vendors and tell them to look for the ones who pay best. Then they can easy find a way to make money. Sometimes they collect to much of same kind and find no vendors want to buy to a price they like and they will have to find something else to collect.I don't yet see the value of the bazaar.
I will call this vendors one of the best add to Siege as they don't add gold to the game as npc vendors on other shards but just help trading.